In a webcast symposium today (July 20) at 2 p.m. EDT (1800 GMT), historians will discuss the legacy of NASA's Viking 1 Mars landing, which occurred on July 20, 1976. Watch the event live here at Space.com, courtesy of NASA TV. 
Main Story: 
Viking on Mars, 40 Years Later: Reflections on Pioneering the Red Planet

From NASA: "The July 19 history talk will include a panel of NASA historians and Roger Launius of the Smithsonian National Air and Space Museum, who will speak about the history of NASA’s Viking missions."

On Wednesday (July 20), NASA will also webcast portions of a daylong Viking 40th anniversary symposium called "From NASA’s First Soft Landing to Humans on Mars." Here's the schedule (all times EDT):

8:15 to 8:45 a.m. — The Exploration of Mars, with NASA Chief Scientist Ellen Stofan
2:50 to 3:35 p.m. — Imagining Living on Mars, with Andy Weir
3:35 to 5:05 p.m. — The Future of Mars Exploration

Our Coverage: 

Remember The Viking: NASA's First Mars Landers

Viking at 40: How NASA Mission Brought Mars Into the Light

Parachutes, Sky Cranes and More: 5 Ways to Land On Mars

Viking 1: The Historic First Mars Landing in Pictures

How to Land on Mars: Martian Tech Explained

From NASA:

"NASA’s Viking Lander 1 successfully reached the Martian surface at 8:12 a.m. July 20, 1976. The Viking 1 and 2 missions collected an abundance of high-resolution imagery of Mars, characterized the structure and composition of the planet’s surface, and analyzed the Martian soil for signs of life, blazing a trail that will one day send humans on our journey to Mars."

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